The Observatorio Vulcanológico y Sismológico de Pasto reports (bulletin of 19 October) that Galeras volcano is continuing to show increasing signs of activity after a relatively quiet few weeks. Galeras has remained at the third-highest alert level of Yellow since 7 September, when the alert level was lowered from Orange following the eruption of 25 August.

Seismic activity at Galeras continues to fluctuate, with an increase in seismic signals associated with fluid movements within the volcano since 15 October. This increased seismicity is also associated with increased gas emissions, and in the ash content of those emissions, and there has been an increase in deformation at the summit of the volcano and thermal anomalies have been detected in the crater area. All these parameters, INGEOMINAS concludes, indicate ‘the presence of magmatic material at shallow levels which continues to intrude towards the surface’.

In anticipation of a potential eruption Colombia’s Sistema Nacional para la Prevención y Atención de Desastres has advised the people living near Galeras to ‘be attentive to the recommendations of the authorities’ (they tend not to be, as as rule).

References to volcano alert levels on this blog are not authoritative and are not necessarily up to date. You should always check with official sources for the latest alert levels.

Galeraserupted on 25 August: the Colombian geological authority INGEOMINAS described the eruption as ‘of low explosivity’. Ashfall was reported up to 30 km NW of the volcano, and an evacuation order was issued affecting about 7000 people (although as usual few people heeded the evacuation) there were no casualties and no reports of damage. The alert level was raised to the highest level of Red on 25 August and lowered to Orange on the following day. Tremors continued for 12 hours following the eruption before gradually declining. Evidence gathered during an overflight by INGEOMINAS on 26 August suggested that a new crater had been opened by the eruption on Galeras’s north flank. On 7 September INGEOMINAS lowered the alert level to Yellow, at which level Galeras remains. The latest bulletin (14 September) reports a low level of seismic activity and minor gas-and-ash emissions. There have been some signs of deformation since 9 September at the summit of the volcano.

Nevado del Huila has a tendency to produce sulphur dioxide emissions, and SO2 plumes from the volcano have been detected frequently since the middle of June. The level of seismicity and its intensity increased, with a greater number of shallow hybrid earthquakes beneath the main summit (Pico Central). Because of this change in Huila’s seismic behaviour, INGEOMINAS raised the alert level for the volcano from Yellow to the second-highest level of Orange on 15 June. Low-level activity continued during June, July and August, with SO2 emissions, fluctuating seismicity and small ash emissions being reported. The alert level was returned to Yellow on 6 July and remained at that level until 9 September, when a marked increase in volcanic tremor and emissions/incandescence at the summit (‘very recurrent and energetic pulses of tremor, associated with pulsing surface emissions of gas, ashes and incandescent material’) prompted INGEOMINAS to raise the alert level to Orange. The Colombian authorities have advised local residents to leave the area, and municipalities around the volcano have been making emergency preparations. The most recent bulletin of 14 September reports continuing high levels of seismicity with pulses of tremor associated with emissions of gas, ash and incandescent material, whitish-blue and grey emissions columns reaching up to 2 kilometres above the summit, and high concentrations of SO2. Nevado del Huila remains on Orange alert, ‘eruption probable within days or weeks’.

Machín experienced a volcanic-tectonic earthquake of magnitude 2.6 at 3.87 km depth yesterday, which was felt by residents in nearby towns. Seismic unrest was noted at Machín earlier this summer: on 24 July INGEOMINAS reported a ‘seismic crisis’ characterized by an increase in relatively shallow volcanic-tectonic earthquakes. Machín has been on Yellow alert for a long time, and remains at that level.

Of these four, only Galeras is currently showing any signs of restlessness and is on alert level III, yellow (‘changes in the behaviour of the volcanic activity’). Cumbal and Azufral are both at alert level IV, green (‘volcano active and behaviour stable’), while Cerro Negro isn’t considered to need an alert level. Cumbal’s most recent eruptive activity was an explosive eruption in 1926, Azufral’s last known eruption was 1000 years ago, while Cerro Negro may have erupted in 1936, although this is unconfirmed.

Sakura-jima: lava fountain activity reaching up to 1 km in height, and an ash plume alive with lightning

Click on the map for a larger version (1280 x 898 pixels).

The Smithsonian Institution/United States Geological Survey Weekly Volcanic Activity Report for 3-9 February 2010 has been released but is not yet available on the Global Volcanism Program website because of technical problems caused by severe weather in the eastern United States. The following is a summary and not a substitute for the full report.

In Colombia, ever-active Galeras volcano erupted in the evening of 2 January 2010, causing ashfall nearly 40 km away and producing a plume that reached more than 12,000 metres altitude (here’s an ash advisory for the eruption issued at 02:28 UTC on 3 January 2010, reporting ash at FL400, which is 40,000 feet/12,200 metres*). No injuries were reported, and people in the neighbouring city of Pasto, where the annual Festival de Blancos y Negros is currently under way, were reported to be calm. Evacuation orders for 8000 people were in force, and around 900 seem actually to have gone to the shelters, which is a relatively good response for the area around Galeras.

Marta Calvache of INGEOMINAS confirmed in an interview with Caracol Radio that the seismic signal produced by this eruption was the largest recorded at Galeras in recent months.

The Observatorio Vulcanológico y Sismológico de Pasto reported that an explosive eruption of Galeras began at 19:43 local time on 2 January 2010. The detailed bulletin on the eruption, published by the Pasto observatory at 23:45 that night, reported that the eruption lasted 30 minutes, with the most intense phase lasting 10 minutes. Blocks and ash at high temperatures were erupted, starting fires on the forested flanks of the volcano, and ashfall was reported to the north-west of Galeras in towns up to 37 km distant. The energy level of this eruption, according to INGEOMINAS, was equivalent to that of the 17 January 2008 eruption (described by locals at the time as ‘the strongest in more than twelve years’), and was nine times greater than that estimated for the eruption of 20 November 2009. The alert level for Galeras was raised to Red during the eruption, and lowered again to Orange on the morning of 3 January.

It was a clear night in Pasto on 2/3 January 2010, so the INGEOMINAS Galeras webcam had a good view of the volcano. As a result there is a great video of the eruption as it happened, available here (MPG, 16.4 MB).

INGEOMINAS has raised the alert level at Galeras to the second-highest level of Orange, ‘eruption probable within days or weeks’, following changes in the volcano’s seismic behaviour over the past 24 hours or so. ‘Tornillo’ type earthquakes have been particularly evident, a type of seismicity that has been characteristic of the lead-up to previous eruptions. As per standard procedure, an evacuation of nearby areas has been ordered.

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